As pointed out in the aforementioned copending application, so-called open clamp structures are known in the prior art which can be installed radially about the object to be fastened. Prior to tightening such open clamp structures, the open ends thereof are interconnected by a mechanical connection. The tightening of the clamp structure may take place by various means, such as, so-called screw-type tightening devices, so-called "Oetiker" ears or by a special construction as disclosed in the aforementioned copending application.
Two principal sources for leakage exist with such types of open clamp structures. On the one hand, leakages may occur because of discontinuities in the form of steps or the like along the inner circumference of the band structure. These problems have been solved effectively by a so-called "stepless" clamp structure as disclosed in my prior U.S. Pat. No. 4,315,348. The other possible source of leakage is the inadequacy of the tightening force with which the clamp structure is closed. In particular, with the availability of plastic materials having a relatively high degree of hardness such as "HYTRELL", which are used in the automotive industry in connection with axle boots, there exists a need for ever increasing tightening forces. The mechanical interconnection disclosed in my prior U.S. Pat. No. 4,299,012 provided an effective solution to the problem of the holding ability of the mechanical interconnection by the use of outwardly extending cold-deformed hooks which take over the force absorption function after a tab-like, transversely extending guide hook guided the inner and outer band portions toward one another during the tightening of the clamp structure. While the mechanical interconnection disclosed in my prior U.S. Pat. No. 4,299,012 proved quite satisfactory, it nevertheless entailed certain disadvantages. The open clamp structures as disclosed for example in FIG. 7 of my prior U.S. Pat. No. 4,299,012 are normally stamped out from flat band material and for reasons of economy are shipped as flat blanks from the place of manufacture to the location of use thereof, for example, an assembly line in an automotive plant where they are preformed into substantially circular shape prior to assembly over the object to be fastened, as disclosed, for example, in my prior U.S. Pat. No. 4,425,781. Since the hooks are normally formed with the use of the same die in the automatic machines manufacturing the flat blank, the angle of the guide hook, which thus has a predetermined angle in the flat blank, will vary in the installed condition, depending on the radius of curvature of the clamping band, i.e., on the diameter thereof. This in turn requires special subsequent attention and remedial action to maintain optimum conditions for the angle of the guide hook in the assembled condition of the clamp. Additionally, the guide hook, which is not intended to absorb any significant tightening forces, is formed by a substantially rectangular tab-like member punched out of the band material, thereby leaving an aperture in the band material corresponding to the area of the punched-out guide hook. This, in turn, may lead to a tendency of the band material to buckle or kink within the area where the band material has been reduced by the punched-out guide hook, when the flat blank is bent into the approximately circular shape of the clamp.